This invention relates to cups for medical electrodes of the type in which a sponge or pad loaded with electrolyte is supported within the cup for contact with the skin of a living patient. More particularly the present invention relates to an improved structure for retaining the electrolyte loaded sponge within the cup.
Prior art structures for retaining or otherwise supporting an electrolyte loaded sponge appear in U.S. Pat. Nos. 542,508; 2,651,304; 3,085,577; 3,762,420 and 3,701,346. In U.S. Pat. No. 542,508, an electrolyte pad is retained in a medical electrode by means of a metal plate affixed to the cup body and with the corners of the plate bent over to form posts to engage a sponge. In the second mentioned patent, an electrolyte pad is retained under a re-entrant lip projecting inwardly from a circular cup-like member. Such constructions are found unsuitable for high volume electrode production due to the labor and the general messiness involved in assembly. Thus the electrolyte pad is preferably loaded with a measured quantity of electrolyte gel and such gel is easily squeezed out of the electrolyte pad when the pad is worked under the corners of the plate in U.S. Pat. No. 542,508 or under the re-entrant lip disclosed in U.S. Pat. No. 2,651,304. The result is a lack of control over the signal transmission capabilities of the electrolyte pad.
U.S. Pat. No. 3,805,577 discloses an absorbent electrolyte pad located under a metallic screen and pierced by prongs 23 which are crimped into a snap fastener member. The manufacturing procedures of piercing and crimping preclude the use of a pregelled electrolyte sponge since gel would be pressed out of the pad.
U.S. Pat. No. 3,762,420 illustrates a metal plate supporting the electrolyte sponge or pad having tabs struck therefrom and bent inwardly upon the margin of the electrolyte pad so as to retain the pad. This manufacturing operation again precludes prefilling of the electrolyte pad with a measured quantity of gel which will not be lost by transfer to other surfaces during the manufacture thereof.
U.S. Pat. No. 3,701,346 solves many of the problems of the foregoing prior art structures by providing a cup which loosely receives a prefilled electrolyte sponge or pad and providing a protective cover which overlays the cup and which has a projection therefrom which biases the prefilled sponge or pad into the cup with a minimum of transfer of electrolyte to the protective cover. A difficulty encountered with such construction is that the prefilled sponge or pad is not positively retained in the electrode cup and, particularly when the use of the electrode has been completed, the prefilled sponge sometimes tends to cling to the skin of the patient and thus falls out of the cup when the electrode is being removed from the patient.